Electrical conductivity of air-exposed and unexposed lead telluride thin films-temperature and size effects
TL;DR: In this paper, it was found that the electrical resistivity of the air-exposed films is much higher than that of the as-grown (unexposed) thin films.
Abstract: Thin films of PbTe of different thicknesses have been prepared on glass substrates at room temperature by vacuum deposition. It is found that the electrical resistivity of the air-exposed films is much higher (by about 2 to 3 orders of magnitude) than that of the as-grown (unexposed) thin films. The electrical resistivity temperature behaviours of both the air-exposed and as-grown (unexposed) thin films of PbTe are different but both show hysteresis behaviour during successive heating-cooling cycles. These observations can be explained by considering that the desorption of absorbed gas molecules (mainly oxygen) and creation of defects at higher temperatures during heating influence the electrical conduction. Further, the time factor involved in gas desorption-adsorption can cause the observed hysteresis in temperature-dependent conduction behaviour. The as-grown (unexposed) thin-film conductivity exhibits the expected reciprocal thickness dependence due to the thickness effect, but the air-exposed film conductivity does not. This can be explained to be due to the complete masking of the thickness effect by the gas adsorption effect in air-exposed film conductivity. The reciprocal thickness dependence observed in the case of unexposed film conductivity has been explained by the 'effective mean free path' model. The low value of the 'grain boundary' mean free path obtained by the analysis points to the fact that in polycrystalline films, grain boundary scattering is extensive and controls the film conductivity.
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TL;DR: In this article, thin films of AgSbTe2 with different thicknesses were prepared by thermal evaporation on glass substrates held at room temperature and the films were all found to be semiconducting in nature.
Abstract: Thin films of AgSbTe2 with different thicknesses were prepared by thermal evaporation on glass substrates held at room temperature. The films were all found to be semiconducting in nature. The film resistivity was found to be a function of inverse thickness and was discussed on the basis of the effective mean free path model. The activation energy was found to be a linear function of the inverse square of film thickness. It was attributed to the quantization of the momentum component of charge carriers normal to the film plane.
9 citations
9 citations
TL;DR: The effect of size and shape of the nanoparticles on thermoelectric properties can be understood on the basis of a carrier-filtering effect that results in an increase in thermopower along with a control over the reduction in electrical conductivity to maintain a high power factor yielding a high figure of merit.
Abstract: The present study aims to see the enhancement in thermoelectric properties of bismuth telluride (Bi2Te3) annealed at different temperatures (573 and 773 K) through silver (Ag) nano-inclusions (0, 2, 5, 10, 15 and 20 wt %). Transmission electron microscopy (TEM) images of Ag incorporated in Bi2Te3 annealed at 573 K shows tubular, pentagonal, trigonal, circular and hexagonal nanoparticles with sizes of 6-25 nm (for 5 wt % Ag ) and 7-30 nm (for 20 wt % Ag). Ag incorporated in Bi2Te3 annealed at 773 K shows mainly hexagonally shaped structures with particle sizes of 2-20 nm and 40-80 nm (for 5 wt % Ag) and 10-60 nm (for 20 wt % Ag). Interestingly, the samples annealed at 573 K show the highest Seebeck coefficient (S, also called thermopower) at room temperature (p-type behavior) for 5% Ag which is increased ca. five-fold in comparison to Ag-free Bi2Te3, whereas for samples with the same content (5% Ag) annealed at 773 K the increment in thermopower is only about three-fold with a 6.9-fold enhancement of the power factor (S2σ). The effect of size and shape of the nanoparticles on thermoelectric properties can be understood on the basis of a carrier-filtering effect that results in an increase in thermopower along with a control over the reduction in electrical conductivity to maintain a high power factor yielding a high figure of merit.
8 citations
01 Dec 2022
TL;DR: In this paper , the AlxSe70Te30-x (x = 0, 15, and 30 wt.%Al) chalcogenide glasses were synthesized and the optical spectra (transmittance T(λ) and reflectance R(λ)) were measured in the range of (300-2500 nm).
Abstract: In the initial step of the current work’s scenarios, the AlxSe70Te30-x (x = 0, 15, and 30 wt.%Al) chalcogenide glasses were synthesized. The alloy-derived thin films with a thickness (∼200 nm) were prepared. The optical spectra (transmittance T(λ) and reflectance R(λ)) were measured in the range of (300–2500 nm). Calculation of the optical parameters included determining the energy bandgap, Eg and tail energy, Ee. The results revealed a decrease in the bandgap energy of the direct transition and an increase in the tail energy with increasing Al-content. The X-ray dispersive analysis (EDX) detected the presence of the elemental components in the three studied systems. As well, by analyzing X-ray diffraction patterns (XRD) and s canning electron microscopy (SEM), the amorphous state of the films was confirmed. In addition, differential scanning calorimetry (DSC) at a heating rate of 5 K/min was used to determine the pre-crystallization and crystallization parameters. For the study of DC conductivity, the temperat ure dependence of sheet resistance was measured and its related parameters were extracted. While, the study of AC conductivity began by measuring the temperature dependence of capacitance and conductance at 5 kHz. Electrical conductivity has been studied in a temperature range of (300–500 K). It was found that there are two types of conduction pathways. The activation energies, Mott parameters, barrier potential energy, and density of localized states around the Fermi level were all evaluated using Mott's variable range hopping model as a benchmark. The dielectric constant, loss factor, complicated electrical modules, and impedance spectroscopy parameters were all shown to be substantially dependent on temperature and Al-content.
7 citations
TL;DR: The effect of defect-order and oxygen stoichiometry on electrical properties of oxygen-deficient perovskites has been demonstrated through the synthesis of BaSrFe2O6−δ (δ = 0.5) as discussed by the authors.
7 citations
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IBM1
TL;DR: In this paper, the total resistivity of a thin metal film is calculated from a model in which three types of electron scattering mechanisms are simultaneously operative: an isotropic background scattering (due to the combined effects of phonons and point defects), scattering due to a distribution of planar potentials (grain boundaries), and scattering by the external surfaces.
Abstract: In this paper, the total resistivity of a thin metal film is calculated from a model in which three types of electron scattering mechanisms are simultaneously operative: an isotropic background scattering (due to the combined effects of phonons and point defects), scattering due to a distribution of planar potentials (grain boundaries), and scattering due to the external surfaces. The intrinsic or bulk resistivity is obtained by solving a Boltzmann equation in which both grain-boundary and background scattering are accounted for. The total resistivity is obtained by imposing boundary conditions due to the external surfaces (as in the Fuchs theory) on this Boltzmann equation. Interpretation of published data on grain-boundary scattering in bulk materials in terms of the calculated intrinsic resistivity, and of thin-film data in terms of the calculated total resistivity suggests that (i) the grain-boundary reflection coefficient in Al is \ensuremath{\approx} 0.15, while it is somewhat higher in Cu; (ii) the observed thickness dependence of the resistivity in thin films is due to grain-boundary scattering as well as to the Fuchs size effect; and (iii) the common observation that single-crystal films possess lower resistivities than polycrystalline films may be accounted for by grain-boundary effects rather than by differences in the nature of surface scattering.
1,842 citations
01 Jan 1938
TL;DR: In this paper, the conductivity of thin films of the alkali metals has been measured in the H. W. Wills Physical Laboratory, Bristol and the experimental results were compared with a formula derived on the basis of this hypothesis.
Abstract: The conductivity of thin films of the alkali metals has recently been measured in the H. W. Wills Physical Laboratory, Bristol*. It was found that as the thickness of the film is decreased to that of a few atomic layers the conductivity drops below that of the bulk metal. In the papers quoted the hypothesis was put forward that this effect is due to the shortening of the mean free paths of the conduction electrons of the metal by collisions with the boundaries of the film. The experimental results were compared with a formula derived on the basis of this hypothesis. This formula was, however, obtained subject to a number of simplifying assumptions, and it is the first purpose of this paper to obtain a more accurate formula. I also compare this formula with experiment, and make certain deductions about the surfaces of thin films.
1,812 citations
TL;DR: In this article, single-crystal films of PbS, pbTe, PbSe, and SnTe have been grown on heated alkali-halide substrates.
Abstract: Single-crystal films of PbS, PbTe, PbSe, and SnTe have been grown on heated alkali-halide substrates. The temperature dependence of the mobility, Hall coefficient, and resistivity between 77\ifmmode^\circ\else\textdegree\fi{}K and 300\ifmmode^\circ\else\textdegree\fi{}K and the dependence of the magnetoresistance upon sample orientation and magnetic field strength at 77\ifmmode^\circ\else\textdegree\fi{}K have been studied. Analysis of the refractive indices, measured interferometrically in the 2.0- to 15.0-\ensuremath{\mu} region, has yielded optical dielectric constants and the direct energy gaps as functions of temperature. These studies indicate that the single-crystal films have electrical and optical properties comparable to those found in bulk material. Discussions of film formation and strain phenomena are presented and compared with the experimental results. Some of the limitations of these materials are discussed with particular emphasis on the role of structure of the films on the electrical properties.
457 citations
TL;DR: In this article, a model for estimating effects due to electron scattering from grain boundaries, occurring simultaneously with background scattering, was developed for polycrystalline metal films in which a very fine-grained structure is often found.
Abstract: A model is developed for estimating effects due to electron scattering from grain boundaries, occurring simultaneously with background scattering. Since grain‐boundary effects are negligible in bulk materials, the model is particularly relevant to polycrystalline metal films in which a very fine‐grained structure is often found. It is shown by solution of the appropriate Boltzmann equation, that the total resistivity can be strongly dominated by grain‐boundary scattering. If grain size increases with film thickness, a marked dependence of resistivity on thickness exists, even when scattering from external surfaces is negligible or is completely specular.
393 citations
TL;DR: In this article, an elementary theory of the optical properties of solids is described, with emphasis on the detailed development of simple models, and the results are expressed in numerical form and the use of meter-kilogram-second units throughout.
Abstract: Publisher Summary This chapter describes elementary theory of the optical properties of solids. One of the most powerful tools for studying the properties of solids is the measurement and analysis of their optical properties. Some of the results required for such an analysis are described in the chapter with emphasis on the detailed development of simple models. It expresses many of the results in numerical form and has dictated the use of meter–kilogram–second (mks) units throughout. The treatment is elementary in the sense that no physics beyond Maxwell's equations and simple quantum mechanics is used in the chapter. Dispersion relations as applied to the analysis of optical properties are discussed in the chapter. It summarizes some of the classical results for two very important physical systems, the free-electron gas and the optical lattice vibrations in ionic crystals. These systems are sufficiently simple that detailed results can be obtained very easily, yet realistic enough that the results give quite a good representation of at least some of the properties of real solids.
292 citations